Solution Self-assembly Behavior Research Articles

Self-Assembly of Thienopyrrole-Fused Thiadiazoles Containing an Amide Linker: Control of Supramolecular Polymerization Mechanism and Chiroptical Properties by Trialkoxy Side Chains.

Three thienopyrrole-fused thiadiazole (TPT) fluorescent dyes featuring a common amide linker and different alkoxy substituents on peripheral trialkoxybenzene moieties were synthesized, and their self-assembly behavior in solution was investigated. The obtained results revealed a substantial steric effect of the alkoxy substituents on the supramolecular polymerization mechanism, which results from a combination of π-stacking and hydrogen (H)-bonding interactions. Detailed spectroscopic measurements revealed that with increasing steric demand of the substituents, the supramolecular polymerization processes in pure methylcyclohexane (MCH) or a mixture of MCH and toluene become temperature-sensitive and enthalpically favorable, resulting in a change from the isodesmic assembly mechanism to the cooperative mechanism. Theoretical calculations suggested that in TPTs with bulky substituents, steric hindrance causes the H-bonding array of the amide moieties to be aligned along the stacking axis of the π-systems; thus, the H-bonding interactions are strengthened compared to those in TPTs with less bulky substituents, compensating for the weakened π-stacking interactions. A chiral TPT derivative with (S) stereogenic centers was found to form homochiral helical supramolecular assemblies that generate discernible circularly polarized luminescence. Achiral TPTs also generate helical assemblies to which preferential helicity can be imparted through the external chiral bias of the solvents (R)- and (S)-limonene.

Oligo(phenyleneethynylene)s: Shape-Tunable Building Blocks for Supramolecular Self-Assembly.

Oligo(phenyleneethynylene)s (OPEs) have attracted widespread attention due to their remarkable (opto)electronic and photophysical properties, which have enabled numerous applications. The versatile functionalization possibilities of OPEs make them unique candidates to form various shape-persistent geometries, including linear, triangular, rectangular, hexagonal and macrocyclic. However, as a result of this structural variety, it is oftentimes challenging to correlate molecular design with self-assembly properties. In this minireview, we have classified OPEs based on their molecular shapes and correlated them with their self-assembly behavior in solution. Particularly, we provide important insights into the aggregation propensity of the different molecular shapes and how to tune the association strength using various non-covalent interactions. Our classification will enable a better understanding of the structure-property correlation in OPEs, which is key to develop supramolecular functional materials.

Self-assembly prediction of architecture-controlled bottlebrush copolymers in solution using graph convolutional networks.

The investigation of bottlebrush copolymer self-assembly in solution involves a comprehensive approach integrating simulation and experimental research, due to their unique physical characteristics. However, the intricate architecture of bottlebrush copolymers and the diverse solvent conditions introduce a wide range of parameter spaces. In this study, we investigated the solution self-assembly behavior of bottlebrush copolymers by combining dissipative particle dynamics (DPD) simulation results and machine learning (ML) including graph convolutional networks (GCNs). The architecture of bottlebrush copolymers is encoded by graphs including connectivity, side chain length, bead types, and interaction parameters of DPD simulation. Using GCN, we accurately predicted the single chain properties of bottlebrush copolymers with over 95% accuracy. Furthermore, phase behavior was precisely predicted using these single chain properties. Shapley additive explanations (SHAP) values of single chain properties to the various self-assembly morphologies were calculated to investigate the correlation between single chain properties and morphologies. In addition, we analyzed single chain properties and phase behavior as a function of DPD interaction parameters, extracting relevant physical properties for vesicle morphology formation. This work paves the way for tailored design in solution of self-assembled nanostructures of bottlebrush copolymers, offering a GCN framework for precise prediction of self-assembly morphologies under various chain architectures and solvent conditions.

Flow-Chemistry-Enabled Synthesis of 5-Diethylboryl-2,3'-bipyridine and Its Self-Assembly Dynamics.

5-Diethylboryl-2,3'-bipyridine (1), which is inaccessible by conventional batch methods, was synthesized by using a flow microreactor. Compound 1 was obtained as an equilibrium mixture of a cyclic trimer and a cyclic tetramer in solution, the latter of which was crystallized in benzene by vapor diffusion of hexane at 7 °C. The dynamic nature of this system was confirmed by solvent- and concentration-dependent experiments. Notably, the dynamics was verified by using flow NMR spectroscopy, which revealed that the time required to reach equilibrium was influenced by the solvent ratio (<18 s, 24-28 s, and 34-42 s in 2 : 1, 1 : 1, and 1 : 2 mixtures of [D6 ]acetone and C6 D6 , respectively). Compound 1 and 3-[4'-(diethylboryl)phenyl]pyridine (2) exhibited different self-assembly behavior in solution and crystals. Density functional theory calculations suggested that this difference was largely due to enhanced planarity between two consecutive aromatic rings.

Synthesis of poly(3-hexylthiophene)-block-poly(phenylisocyanide) copolymers and their self-assembly in solution

Controlled synthesis of new P3HT-b-poly(phenylisocyanide) copolymer was developed under nickel-catalyzed coordination polymerizations, and their solution self-assembly behaviors were revealed.

Effects of Hydrophobic Modifications on the Solution Self-Assembly of P(DMAEMA-co-QDMAEMA)-b-POEGMA Random Diblock Copolymers.

In this work, the synthesis and the aqueous solution self-assembly behavior of novel partially hydrophobically modified poly(2-(dimethylamino) ethyl methacrylate)-b-poly(oligo(ethylelene glycol) methyl ether methacrylatetabel) pH and temperature responsive random diblock copolymers (P(DMAEMA-co-Q6/12DMAEMA)-b-POEGMA), are reported. The chemical modifications were accomplished via quaternization with 1-iodohexane (Q6) and 1-iodododecane (Q12) and confirmed by 1H-NMR spectroscopy. The successful synthesis of PDMAEMA-b-POEGMA precursor block copolymers was conducted by RAFT polymerization. The partial chemical modification of the diblocks resulted in the permanent attachment of long alkyl chains on the amine groups of the PDMAEMA block and the presence of tertiary and quaternary amines randomly distributed within the PDMAEMA block. Light scattering techniques confirmed that the increased hydrophobic character results in the formation of nanoaggregates of high mass and tunable pH and temperature response. The characteristics of the aggregates are also affected by the aqueous solution preparation protocol, the nature of the quaternizing agent and the quaternization degree. The incorporation of long alkyl chains allowed the encapsulation of indomethacin within the amphiphilic diblock copolymer aggregates. Nanostructures of increased size were detected due to the encapsulation of indomethacin into the interior of the hydrophobic domains. Drug release studies demonstrated that almost 50% of the encapsulated drug can be released on demand by aid of ultrasonication.

UV-stabilized self-assembled amphiphilic triblock terpolymers supramolecular structures with low cytotoxicity as doxorubicin carriers.

Amphiphilic polystyrene-b-poly[(7-(Allyloxy)-2H-chromen-2-one)-co-(2-hydroxyethyl methacrylate)]-b-poly(2-(dimethylamino)ethyl methacrylate) (PS-b-P(AC-co-HEMA)-b-P(DMAEMA)) triblock terpolymers were synthesized by atom transfer radical polymerization (ATRP). PS-b-P(AC-co-HEMA)-b-PDMAEMA triblock terpolymers were characterized using proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). The effect of various pH values on solution self-assembly behavior of PS-b-P(AC-co-HEMA)-b-P(DMAEMA) triblock terpolymers was investigated. Field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), fluorescence microscopy, and dynamic light scattering (DLS) were used to observe the size and morphology of the assembled triblock terpolymers. With altering pH value, different morphologies were obtained including spherical micelles, Janus snowman, and spherical Janus as well as cubic-hexagonal structures. UV light was used to stabilize the self-assembled morphologies and FE-SEM results showed that morphology remained unchanged after photo-dimerization. The self-assembled triblock terpolymers before and after photo-crosslinking were loaded with doxorubicin (DOX) and drug release behavior was examined at different conditions. Due to photo-crosslinking of self-assembled terpolymers, cumulative release was decreased. Thus, they might be more controllable drug carriers in drug delivery systems.

Tunable low-dimensional self-assembly of H-shaped bichromophoric perylenediimide Gemini in solution.

A material with diverse self-assembled morphologies is extremely important and highly desirable because such samples can provide tunable optical and electronic properties, which are critical in applications such as organic photovoltaics, microelectronics and bio-imaging. Moreover, the synthesis and controllable self-assembly of H-shaped bichromophoric perylenediimides (PDIs) are needed to advance these materials in organic photovoltaics, microelectronics and bio-imaging; however, this has remained a great challenge thus far. Here, we successfully synthesize a novel H-shaped bichromophoric PDI Gemini through the palladium-catalyzed coupling reaction. The as-prepared PDI Gemini exhibited unprecedented tunable self-assembly behavior in solution, yielding diverse low-dimensional superstructures, such as one-dimensional (1D) helices, two-dimensional (2D) rectangular nanocrystals, pyramid-shaped parallelograms, ultralarge micro-sheets, and uniform nanospheres, under different self-assembly conditions. Of particular interest, the 2D hierarchical superstructures along with their formation mechanisms represent the first finding in the self-assembly of PDI-based molecules. This study opens a new avenue for tunable self-assembly of conjugated molecules and affords opportunities for the fabrication of novel self-assembled optical and electronic materials based on PDI molecules.

Solution self-assembly of ABC triblock terpolymers with a central crystallizable poly(ferrocenyldimethylsilane) core-forming segment

The synthesis and solution self-assembly behavior of a range of linear ABC triblock terpolymers with a central crystallizable poly(ferrocenyldimethylsilane) core-forming segment have been explored.

Tracking self-assembly morphology of cationic peptide analogues using turbidimetric- potentiometric titration

Peptide amphiphiles are promising molecular materials for drug delivery systems and regenerative medicine through formation of well-ordered nanostructures. Rationally designed self-associating synthetic peptide analogues containing arginine (FEFEFRFR) and lysine (FEFEFKFK) were studied to understand the effect of pH and side chain interactions and its influence on the resulting nanostructure formation. Changes in structural conformation in bulk were followed by turbidimetric-potentiometric titrations with pH ranges from 4 to 11 and 4 to 12.6 for FEFEFKFK and FEFEFRFR respectively. Fourier Transform Infrared Spectroscopy (FTIR) was used to determine the secondary structure of the peptides while Field Emission Scanning Electron Microscopy (FE-SEM) was employed to study the morphology and dimension of higher order structures at various pH. Turbidity results showed that both FEFEFKFK and FEFEFRFR displayed higher turbidity level when their side chains were neutralized, in which FEFEFRFR showed higher turbidity level when arginine was neutralized. Both peptides exhibited similar self-assembly behavior in solution which mainly adopted antiparallel β-sheets conformation with spherical structures of different micro-metre size when there is a net charge of +2 or -2. FEFEFKFK was also found to form concaved disks and beads-on-a-string arrangement at pH 4. Both the peptide analogues were capable of forming smaller aggregates in a network of spherical structure at nanoscale when the net charge was near zero. This study ultimately provides a better understanding of predicting morphology and size of surface functional modification of self-assembled polypeptides.

Self-Seeding of Block Copolymers with a π-Conjugated Oligo(p-phenylenevinylene) Segment: A Versatile Route toward Monodisperse Fiber-like Nanostructures

Three well-defined crystalline–coil diblock copolymers of oligo(p-phenylenevinylene)-b-poly(N-isopropylacrylamide) (OPV5-b-PNIPAM18, OPV5-b-PNIPAM49, and OPV5-b-PNIPAM75; the subscripts represent the number of repeat units of each block) with the same crystallizable core-forming OPV segment but different corona-forming PNIPAM blocks of various chain lengths were synthesized. Their solution self-assembly behavior was examined in methanol, ethanol, and isopropanol. Both the solvent and the length of the PNIPAM block were found to affect the self-assembly of the block copolymers. In methanol, OPV5-b-PNIPAM18 formed a mixture of fiber-like micelles of uniform width and two-dimensional platelet-like structures with fiber-like micelles protruding from the ends. In ethanol and in isopropanol, this polymer only formed long fiber-like micelles of uniform width. OPV5-b-PNIPAM49 formed long fiber-like micelles (several micrometers) of uniform width in all three solvents, but under the same self-assembly conditions, ...

Synthesis of Mikto-Arm Star Peptide Conjugates.

Mikto-arm star peptide conjugates are an emerging class of self-assemblingpeptide-basedstructural units that contain three or more auxiliary segments of different chemical compositions and/or functionalities. This group of molecules exhibit interesting self-assembly behavior in solution due to their chemically asymmetric topology. Here we describe the detailed procedure for synthesis of an ABC Mikto-arm star peptide conjugate in which two immiscible entities (a saturated hydrocarbon and a hydrophobic and lipophobic fluorocarbon) are conjugated onto a short β-sheet forming peptide sequence, GNNQQNY, derived from the Sup35 prion, through a lysine junction. Automated and manual Fmoc-solid phase synthesis techniques are used to synthesize the Mikto-arm star peptide conjugates, followed by HPLC purification. We envision that this set of protocols can afford a versatile platform to synthesize a new class of peptidic building units for diverse applications.

Self-assembly of poly(vinylidene fluoride)–polystyrene block copolymers in solution: Effects of the length of polystyrene block and solvent compositions

We report the first preliminary and extensive study on the solution self-assembly behaviors of poly(vinylidene fluoride)–b-polystyrene (PVDF–PS) block copolymers. The two PVDF–PS polymers we examined have the same length of PVDF block with number averaged repeating unit of 180, but distinctly different lengths of PS block with number averaged repeating unit of 125 and 1202. The self-assembly experiments were carried out in a series of mixture solutions containing a good solvent N,N-dimethylformamide and a selective solvent with different ratios. Our results showed that the self-assembly process was greatly affected by the two factors we examined, i.e. the length of the PS block and the solvent composition. We hope that our study could stimulate more research on the self-assembly of PVDF-containing polymers in solution.

Tunable amphiphilic graft copolymers bearing fatty chains and polyoxazoline: synthesis and self-assembly behavior in solution

Synthesis and self-assembly behavior in solution of tunable copolymers with amphiphilic grafts based on fatty chain polymethacrylate and polyoxazoline.

Pathway Complexity in the Enantioselective Self-Assembly of Functional Carbonyl-Bridged Triarylamine Trisamides.

Functional supramolecular systems like carbonyl-bridged triarylamine (CBT) trisamides are known for their long-range energy transport at room temperature. Understanding the complex self-assembly processes of this system allows for control over generated structures using controlled supramolecular polymerization. Here, we present two novel CBT trisamides with (S)- or (R)-chiral side chains which show a two-pathway self-assembly behavior in solution. Depending on the thermal profile during the self-assembly process, two different stable states are obtained under otherwise identical conditions. A kinetically trapped state A is reached upon cooling to 7 °C, via a proposed isodesmic process. In addition, there is a thermodynamically stable state B at 7 °C that is induced by first undercooling to -5 °C, via a nucleation-elongation mechanism. In both cases, helical supramolecular aggregates comprising H-aggregated CBTs are formed. Additionally, controlled supramolecular polymerization was achieved by mixing the two different states (A and B) from the same enantiomer, leading to a conversion of the kinetically trapped state to the thermodynamically stable state. This process is highly enantioselective, as no conversion is observed if the two states consist of opposite enantiomers. We thus show the importance and opportunities emerging from understanding the pathway complexity of functional supramolecular systems.

A pillar[6]arene-based [2]pseudorotaxane in solution and in the solid state and its photo-responsive self-assembly behavior in solution.

A pillar[6]arene-based [2]pseudorotaxane was constructed in solution and studied in the solid state, and its photo-responsive self-assembly behavior in solution was investigated.

Self-assembly of amphiphilic macrocycles containing polymeric liquid crystal grafts in solution

Amphiphilic macrocycles containing polymeric liquid crystal side-chains are synthesized facilely, and the topological effects on their solution self-assembly behaviors are investigated, compared with their linear analogues.

Multifunctional Block Copolymer: Where Polymetallic and Polyelectrolyte Blocks Meet

Sequential reversible addition–fragmentation transfer (RAFT) polymerization of a mixed sandwich cobaltocene monomer (η5-cyclopentadienyl-cobalt-η4-cyclobutadiene (CpCoCb)) and a phosphonium salt functionalized styrene monomer resulted in the first example of a unique multifunctional block copolymer consisting of a metallopolymer block and a polyelectrolyte block. The polyelectrolyte block was decorated with a gold anion (AuCl4–) via salt metathesis, resulting in a heterobimetallic block copolymer with distinct gold and cobalt sections. Solution self-assembly behavior of this unique metallopolymer-b-polyelectrolyte copolymer before and after salt metathesis was studied. Heterobimetallic micelles with a gold containing core and a cobalt-containing corona were obtained, and then the core was reduced to form gold nanoparticles (AuNPs). Studies on the solid-state self-assembly of this unique block copolymer showed that it phase separated into hexagonally packed cylinders. Salt metathesis of the phase-separated...

Dinonylphenyl end-capped poly(ethylene glycol)-b-polystyrene: synthesis and its unusual crystalline and self-assembly behaviors

Block copolymers, dinonylphenyl end-capped polyethylene glycol-b-polystyrene (DNPE-PEO-b-PSs) were synthesized in a one-step atom transfer radical polymerization (ATRP) of styrene. The PEO block in the DNPE-PEO-b-PS samples (volume fraction of PS: 66.8–93.2 %) was found to be amorphous, which contrasts with DNPE-PEO precursor, traditional methoxide end-capped polyethylene glycol-b-polystyrene (PEO-b-PS) and dinonylphenyl end-capped poly-(ethylene glycol)-b-poly(fluorinated methyl methacrylate)(DNPE-PEO-b-PFMAs). Meanwhile, DNPE-PEO-b-PSs display an intriguing self-assembly behavior in solution. Block copolymer particles with mesoporous internal structures are directly formed by self-assembly of DNPE-PEO-b-PS in tetrahydrofuran/water solutions. It is proposed that DNPE end group has an important effect on the crystallization of the block copolymers as well as their self-assembly behaviors in solution.

Crystallization-Driven Solution Self-Assembly of μ-ABC Miktoarm Star Terpolymers with Core-Forming Polyferrocenylsilane Blocks

A comparative study of the solution self-assembly behavior of two polystyrene-arm-polyisoprene-arm-polyferrocenylsilane (μ-SIF) miktoarm star terpolymers of similar composition has been conducted: one with a short, atactic, noncrystallizable poly(ferrocenylethylmethylsilane) (PFEMS) block (μ-SIFa) and one with a short, crystallizable poly(ferrocenyldimethylsilane) (PFDMS) block (μ-SIFc). Both solvent composition and the amorphous/crystallizable nature of the polyferrocenylsilane (PFS) block exhibited a profound influence on the morphologies of the micelles obtained. In hexane, the formation of uniform spherical micelles with an amorphous, phase-mixed PS/PFS core was observed for both μ-SIFa and μ-SIFc. The introduction of cyclohexane (a theta-solvent for PS at 34.5 °C) to give a 1:1 cyclohexane/hexane (v/v) solvent composition resulted in the formation of distorted spherical micelles with a core composed of phase-separated PS and PFS, for both μ-SIFa and μ-SIFc. Interestingly, the distorted spherical micelles formed from crystallizable μ-SIFc evolved with time into elongated fiber-like structures with a phase-separated PS and PFDMS core, while the noncrystallizable counterpart, μ-SIFa, remained as distorted spheres. It was found that in ethyl acetate, a good solvent for PI and PS, μ-SIFa remained unimeric in solution, whereas μ-SIFc formed cylindrical micelles composed of a crystalline PFDMS core and a phase-separated, patchy, PS and PI corona. Finally, seeded growth of μ-SIFc from short, cylindrical PFDMS-b-PDMS seeds (PDMS = polydimethylsiloxane) was demonstrated, yielding B–A–B block comicelles where outer segments derived from μ-SIFc blocks bore a strong resemblance to that ultimately formed under conditions of homogeneous nucleation.